1. Field of the Invention.
The invention relates to apparatuses for cleaning bag-type or cartridge-type fabric filters employing pulses of compressed air.
2. Description of the Related Art.
Fabric filters are increasingly being used in many industries to remove particulates from industrial process gas streams. Due to tightening environmental regulations, fabric filters are often the only particulate control apparatus capable of bringing an industrial process into compliance with the laws.
In practice, fabric filters are most often formed into tall cylindrical bags which are placed over cylindrical wire cages of substantially the same size. The wire cylinders restrain the bags in their cylindrical shape. A number of these bags and cylinders are joined at the top by a tube sheet The assembly is secured within a bag house. In operation, particulate-laden gas is forced through or drawn into the bag house. The gas is forced through the filters, up through the center of the cages, out the tube sheet, and then out of the bag house. Particles remained trapped on the outside of the filter bags. If left uncleaned, the particles would soon clog the filter and prevent gas from flowing through.
To clean the filters, the most prevalent method is to periodically blow compressed air through the center of the bags. The compressed air is directed through a header apparatus, through pulse valves, and out a number of blow tubes that are centered over the bags. The compressed air temporarily inflates the bags, thereby blowing the particles off and into a hopper at the bottom of the bag house.
An improvement to this basic design is disclosed in U.S. Pat. No. 4,033,732, that was issued to Axelsson et al, on Jun. 5, 1977. This apparatus incorporated the pulse valve into the header in order to improve performance. The apparatus disclosed by Axelsson, however, requires a great deal of machining and other fabrication to make the header.
It is common in the art for blow tubes to be controlled by individual valves connected to a common header that permit the bags to be cleaned in sequence. Use of these apparatuses is very expensive, however. Blow tubes must be either welded or mechanically fastened to the header. The holes through which the blow tubes protrude must be precisely machined on a header that runs the entire length of the tube sheet. Any mistake on such a large and complex pressure vessel is very costly for the entire system, since the cost of the header apparatus often represents 10% of the cost of the bag house.
What is needed, therefore, is a header apparatus that is much more inexpensive to manufacture, is less likely to results in manufacturing mistakes, and for which manufacturing mistakes can be easily corrected.